The ending of Flash Boys enigmatically mentions a microwave transmission tower in Pennsylvania, saying it exemplifies yet another tale of Wall Street greed and hypocrisy. High Frequency Trading is all about milliseconds. If a HFT trading bot gets actionable information a few milliseconds before everyone else, it will act and profit from it. This is especially true of futures trading information from Chicago arriving at New York stock trading desks. Futures trading leads stock prices (not the other way way around.)

Fiber used to be the fastest way to get data from Chicago to NYC. It is being replaced by microwave. Ann Brocklehurst helps explain what Lewis is hinting at.

There are also microwave networks between Chicago and Washington, D.C., where economic news and indicators, are regularly announced by government agencies. To get their hands on this information as quickly as possible, several HFT shops even set up not just their own private microwave networks but also their own “news agencies.”

From the comments:

The microwave device number can be found by searching the tower location in the application database on the FCC website. Lewis was possibly suggesting that it is hypocritical for a company assisting the SEC by making its watchdog program (Midas) while at the same time installing a Chicago to Jersey microwave link to game the system via HFT methods